1. Field of the Invention
This invention relates to the field of animal housing, and most advantageously to the housing, servicing and transportation of laboratory animals requiring isolation from contagion or isolation of contagion, using individually removable animal cage units.
2. Description of the Prior Art
In the art of housing animals, multi-unit systems are employed for a variety of applications. These applications range from pet stores to demanding laboratory experimentation. Problems that develop when confining a large number of animals in close proximity with one another include unpleasant odors, inadequate air supply, cross-infection and difficulty with installation and removal of individual cage units. In laboratory experimentation applications, animals are usually divided into a subject group and a control group, the subject group receiving a treatment under investigation while the control group is spared. When the subject group in an experiment is subjected to disease organisms, valid experimental results demand that the control group have absolutely no exposure to the disease in question. In addition, completely pathogen-free animals are required for some experiments. Production of such ultra-pure animals requires the ultimate in isolation.
Housing a large number of animals poses problems in supplying animals with basic needs such as air and food, as well as the aforesaid problem of infection. In some prior art systems, banks of animal units have been individually fitted with pipe connections to supply and exhaust air, and sometimes to flush refuse from the animal housing unit. When a large number of animal units are mounted in a relatively small space, this maze of individual connections can be a nightmare for the person servicing the animals. This problem is only partially solved in systems that employ press-fit tube connections. On insertion of an animal unit in a system employing press-fit connections, the installer must visually line up the receptacle in the animal unit with the pipe in the rear of the mounting rack before the cage can be put in its final position. Inexact lineup of cages wastes supply air, may introduce pathogens, and may release contagion-bearing exhaust air. The complexity and inconvenience of individually piped systems clearly generates a substantial expense upon purchase and with continuing use, to laboratories that employ them.
In less demanding applications where some cross-ventilation can be tolerated, former animal housing systems have often employed laminar flow ventilation. In laminar flow ventilation systems, air is supplied via a plenum over an entire bank of animal units. Theoretically, in such a system all the portions of cage ventilation air move parallel to all the other portions, out of the plenum and across the animal units. It is intended that each cage unit receive air directly from the plenum, and discharge air without cross-ventilation to or from other units. Practically, the laminar flow ventilation method is not particularly effective at eliminating cross-ventilation. Discontinuities encountered in the path of the air mass generate eddy currents which preclude uniform air motion. Eddy currents and surface currents produce a random movement of air, sometimes directly opposite the movement of the larger directed air mass. This phenomenom is analogous to the way a canoeist can be more easily carried up river by staying close to the river bank.
Laminar air flow systems are generally designed to supply clean air across a bank of cages, then direct the air into the room where the animal housing system is kept. When laminar air flow systems are so designed to exhaust into the room, persons allergic to the dander of laboratory animals, and all persons in installations where communicable disease experiments are carried out, must be equipped with personal protective equipment. If a plenum is used both on the air supply side and on the exhaust side, not only will the animals be enclosed and unobservable, but insertion and removal of animal units will be extremely inconvenient.
It will be appreciated that problems with cross-ventilation and problems with convenience of installation and removal often involve a trade-off. If a system is completely airtight, installation and removal are likely to be inconvenient, requiring connection or disconnection of some sort of coupling. Conversely, a system which features convenience of installation and removal will generally do so at the expense of dependable, airtight couplings. The present invention seeks to resolve this dichotomy in a system applicable to a range of applications.
The present invention provides a system whereby the cross-ventilation advantages of an individually-piped system are obtained, as well as the installation and removal convenience of a one-sided laminar flow system. The animal cages are individually removable, yet tapered flanges and gasketing allow the cages to be fitted tightly against the supply and exhaust ducts in a way as effective at reducing cross-ventilation as the individual piping method. Baffles may be mounted in the air ducts to minimize eddy and surface currents, and also help to minimize any cross-ventilation. For the most demanding applications, an airtight valve arrangement provides safe and secure connection. The support rack for the unit is hollow and also serves the function of duct work for supply of air to the individual cages and exhaust therefrom. The system is thus compact and convenient, solving both cross-ventilation and installation-removal problems in one.
Finally, the system is widely applicable due to inexpensive yet sturdy and dependable construction. In simple embodiment, it is useful in pet stores and non-demanding laboratory work. In a strongly-constructed unit, it is useful as a portable environment for shipping animals. In the most demanding laboratory contagious disease experiments, the full panoply of sealed cages and valves can be used in conjunction with an isolation work chamber for maximum protection. The isolation work chamber is adapted to interface with the cage rack whereby individual cages can be withdrawn, serviced and reinserted. The total system thus can be employed to produce pathogen-free animals or to conduct communicable disease experiments, in addition to merely housing and transporting animals.